11.1-11.2 binomial theorem & binomial expansion. pascal’s triangle
TRANSCRIPT
11.1-11.2 Binomial Theorem & 11.1-11.2 Binomial Theorem & Binomial ExpansionBinomial Expansion
Pascal’s Triangle
Pascal’s Triangle with even and odd numbers colored differently:
Expanding Binomials…
What pattern(s) do you see?.....
543223455
4322344
32233
222
1
0
510105 )(
464 )(
33 )(
2 )(
)(
1 )(
babbababaaba
babbabaaba
babbaaba
bababa
baba
ba
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
1 7 21 35 35 21 7 1
1 8 28 56 70 56 28 8 1
1 9 36 84 126 126 84 36 9 1
Use this triangle to expand binomials of the form (a+b)n. Each row corresponds to a whole number n. The first row consists of the coefficients of (a+b)n when n = 0.
Example 1
Example 2
Expand (a + b)6
• 1 6 15 20 15 6 1 (coefficients from Pascal’s triangle)
• 1a6 6a5 15a4 20a3 15a2 6a1 1a0 (exponents of a begin with 6 and decrease)
• 1a6b0 6a5b1 15a4b2 20a3b3 15a2b4 6a1b5 1a0b6
(exponents of b begin with 0 and increase by 1)• a6 + 6a5b + 15a4b2 + 20a3b3 + 15a2b4 + 6ab5 + b6
(expansion in standard, simplified form)
Return to Triangle
Expand (x – 2)3
• 1 3 3 1 (coefficients from Pascal’s triangle)• 1a3 3a2 3a1 1a0 • 1a3b0 3a2b1 3a1b2 1a0b3
• Now substitute x for a and –2 for b:• 1(x)3(–2)0 3(x)2(–2)1 3(x)1(–2)2 1(x)0(–2)3
• x3 – 6x2 + 12x – 8 (expansion in standard, simplified form)
Return to Triangle
(let a = x and b = –2)
Factorial Notation
! ( 1)( 2)( 3).......(3)(2)(1)n n n n n
7! 7(6)(5)(4)(3)(2)(1)
4! (4)(3)(25 5 )( ) )(1
Read as “n factorial”
8!
6!
0! 1
8(7)(6!)
6! 8(7) 56
Finding a particular term in a Binomial Expansion:
!
( )! !n r rn
a bn r r
9
6 3
!
! !
9 8 7 6
6 3 2 1
( )( )( !)
!( )( )( )
Ex.: Find the 4th term in expansion of (a + b)9:
This is the 4th term, so value of r (b’s exponent) is 4 – 1 = 3.
This means the exponent for a is 9 – 3, or 6.
So, we have the variables of the 4th term: a6b3
Formula for finding a particular term in expansion of (a + b)n is:
Coefficient is: 6 384a b
Finding a particular term in a Binomial Expansion:
!
( )! !n r rn
a bn r r
12
5 7
!
! !
12 11 10 9 8 7
5 4 3 2 7
( )( )( )( )( !)
( )( )( )( !)
Ex.: Find the 8th term in expansion of (2x – y)12:
This is 8th term, exponent for b is 8 – 1 = 7.
This means the exponent for a is 12 – 7, or 5.
So, the variables of the 8th term: a5b7,
Formula for finding a particular term in expansion of (a + b)n is:
Coefficient: 5 7792 32x y ( )( )
or (2x)5(–y)7.
5 725344x y